Digital governor

ABSTRACT

Electronic governors for controlling the speed of prime movers wherein signals corresponding in frequency to actual speed and desired speed are compared to produce an error signal for controlling a prime mover actuator in accordance with the time integral of the period difference between the compared signals, the rate of integration and overall gain of the governor servo loop being completely independent of the actual speed of the prime mover. Alternative governors are disclosed which include droop and isochronous versions as well as a governor featuring proportional plus integral control. All embodiments are entirely digital in design and inherently immune to drift due to temperature and power supply variations.

United States Patent 1191 Barrett DIGITAL GOVERNOR PrimaryExaminer-Edgar W. Geoghegan Assistant Examiner-H. Burks Sr. [76]Inventor: William J. Barrett 2960-Imper1al Oak Dr Rockford, m 61614Attorney, Agent, or Firm-Wolfe, Hubbard, Leyd1g,

V01t & Osann Ltd. [22] Filed: Sept. 2, 1971 1 PP 177,235 [57] ABSTRACTElectronic governors for controlling the speed of [52] US. Cl ..60/664,318/318 prime movers wherein Signals corresponding i f [51] Int. Cl.F0ld 25/32, FOlb 25/16 quency to actual Speed and desired speed are [58]Field of Search 60/105; 415/17, 30; pared to produce an error signal forcontrolling a 1, 235/151; 318/318 prime mover actuator in accordancewith the time integral of the period difference between the compared[56] References C'ted signals, the rate of integration and overall gainof the UNITED STATES PATE TS governor servo loop being completelyindependent of 3,174,504 3/1965 Rosenbrock 137/486 the a u sp f th primemoverv Alternative gov- 3,097,488 7/1963 Eggenberger 60/105 ernors aredisclosed which include droop and isochro- 3,097,490 7/1963 Callan eta1.... 60/105 nous versions as well as a governor featuring propor-3,552,872 1/1971 Giras et a1. 415 tional plus integral control. Allembodiments are en- 3,572,959 3/1971 Shaughnessy 415/30 1 digital indesign and inherently immune to drift due to temperature and powersupply variations.

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SHEET, l 0F 15 DIGITAL GOVERNOR The present invention relates in generalto apparatus for controlling the speed of prime movers and morespecifically to electronic speed control governors employing digitaltechniques.

The primary function of speed governors is to maintain the speed ofprime movers essentially constant during variations in the load on theprime mover. Conventional speed governors employ a reference signalrepresenting the desired or set point speed. To this signal is compareda signal corresponding to the actual speed of the prime mover, thedifference between these signals resulting in a servo correction signalfor controlling, through an appropriate autuator, the energy flow to theprime mover to correctively adjust the speed and thereby to reducedeviations between the compared signals to zero. The performance of atypical governor in responding to speed changes to produce a correctionsignal is measured by the speed of correction or free dom from lag, thestability of control and the immunity from drift in operation due to theeffects of temperature, aging, and power supply variation on componentsof the system. The speed governors heretofore available in the art werelimited in their capacity for improvement in accordance with the abovecriteria in that they were inherently analog devices, relying on thestability and accuracy of discrete signal levels at all stages ofdecision and control within the system. These discrete signals, be theymechanical, electrical or hydraulic signals, were inherently dependentfor their reliability on devices subject to the above-mentionedenvironmental factors.

Accordingly, it is the primary object of the present invention toprovide a speed governor for prime movers which is inherently immune todrift in its operating characteristics due to temperature, aging, andpower supply variations. It is a related object to provide such agovernor which is nonetheless characterized by fast response andexcellent stability over wide ranges of load variations on the primemover.

It is another object of the present invention to provide an electronicgovernor which is all-digital in design and which relies to only aminimal extent on the stability of discrete components within thesystem.

There are two basic types of governors, droop governors and isochronousgovernors. A droop" governor controls energy flow to the prime mover ina fashion such that as load torque on the prime mover (operating as asingle unit) increases, the steady state speed decreases from theno-load set point value. For a given set point, there is a particularsteady state speed which obtains for each value of load. Droop governorsare employed principally to control prime movers driving alternatorsconnected in parallel and thus subjected to synchronizing torque, atleast one governor-prime mover-alternator system being isochronous tomaintain the electrical system frequency. By adjusting the set pointsignal of a droop governor so connected to control a prime mover drivingan on line alternator, the share of system load provided by thatalternator is changed. An isochronous governor, on the other hand,simply controls the rate of energy flow to the prime mover to makeactual speed equal to set point speed, and thus to make the steady statespeed error substantially zcro. Time integral and time derivative signalcomponents may be utilized to reduce transient times and inhibithunting. As such, an isochronous governor is inherently droop-free."

A further object is the provision of an all-digital design technique andapparatus which is applicable to the various common forms of governorcontrols, including both droop and isochronous governors, with equaleffectiveness and with a minimum of complexity in converting from oneform of control to the other.

Still another object of the present invention is the provision of agovernor responding to speed variations of a prime mover at a rate andin an amount which is dependent only on speed variations and which isessentially independent of the adjusted value of the nominal steadystate set point speed at which the prime mover is being maintained.

Another object is the provision of an all-digital electronic governorcharacterized by proportional control for an immediate response to loadchanges and resulting speed errors and integral control for reducingspeed errors during prolonged off-speed periods.

It is a further object to provide a governor in which two periodicallyrecurring signals respectively proportional in frequency to the actualspeed of the prime mover and the desired set point speed are compareddigitally to signal a number proportional to the integral of thedifference in their respective periods.

A more specific object is the provision of digital signal comparingapparatus including a counter controlled to repetitively compare tworecurring wave trains by counting up and down respectively duringnon-coincident periods of the respective wave trains, with the attendantadvantage that the count in the counter at the end of each comparisonoperation provides a digital representation of the time integral of thedifference in the periods of the respective wave trains. A relatedobject is the provision of such signal comparison apparatus in which thecounter capacity is minimized without loss of comparison accuracy byrendering the counter inoperative during the actual overlap of the twoperiods being compared during any given comparison operation.

An ancillary object of the present invention is the provision of a speedgovernor in which all internal computations are performed digitally, butwhich nonetheless is suitable for use with conventionalelectromechanical actuators. More specifically, it is an object toprovide such a governor in which an electrical output signal suitablefor driving an analog actuator is provided having an average d.c.content which is proportional to a digitally computed numberrepresenting the desired energy flow.

Yet another object of the present invention is the provision of avariable frequency oscillator for producing a speed reference signalhaving a period corresponding to the algebraic sum of a plurality ofbinary coded input signals. It is a related and more specific object toprovide a variable frequency oscillator in which a binary up-downcounter is employed and controlled to consecutively monitor a pluralityof input signals and to count in a direction and for a periodcorresponding respectively to the sense and binary magnitude of each ofsaid input signals, with the advantage that the time interval requiredfor completing the sequence of monitoring each input signal and countingup or down for periods corresponding to the binary magnitude of eachsignal is linearly related to the algebraic sum of the binary numbersrepresenting the values of the respective signals.

Other objects and advantages of the present invention will becomeapparent upon reading the following description, taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a simplified block diagram of an isochronous governorconstructed in accordance with the present invention, showing thecontrol equations associated with the various functional elements.

FIG. 2 is a block diagram of a modified version of the governor shown inFIG. 1 which is operational as a droop governor.

FIG. 3 is a block diagram of amodification of the governor shown in FIG.2 illustrating the duplication of existing hardware for converting thegovernor of FIG. 2 into an isochronous governor.

FIG. 4 is a block diagram of a further modification of the governor ofFIG. 2.

FIG. 5 is an explanatory diagram showing the manner in which FIGS. 6a-6fmay be joined to form a composite, detailed schematic diagram of thegovernor shown by the generalized blocks in FIGS. 1-4.

FIGS. 6a-6f are detailed schematics of the actual circuits used in thegeneralized block shown in FIGS. 14.

FIGS. 713 are timing diagrams illustrating the operational features ofthe various circuits of FIGS. 6a-6f. While the invention has been shownand will be described in connection with certain preferred embodimentsthereof, there is no intention that the invention is to be limited tothe particular embodiments set forth.

On the contrary, it is intended to cover the various modifications,alternatives and equivalents falling within the spirt and scope of theinvention.

AS used herein, the term signal is to be taken in a generic sense and isintended to include any electrical manifestation having informationcontent. Thus a signal may be a voltage or current carriedby two linesor it may. be the parallel combination of binary bits presentedsimultaneously on a plurality of lines equal to the number of bits. Inthe former case the magni tude of the signal is measured in terms ofcurrent, voltage, frequency or period, whereas in the latter case themagnitude of the signal is measured by the binary numberrepresented bythe simultaneously occuring logic states on the parallel lines.

The logic elements shown in connection with the following descriptiontypically operate between supply voltage levels of UV. and 5v., and inthe descriptionto follow a logic I is assumed to be the 5v. level, whilea logic 0 is the 0v. level.

In certain drawings digital circuit elements have been symbolicallyillustrated in the manner commonly used in the electronics art. In viewof the widespread usage of certain elements, it is unnecessary to give adetailed description of the combination of components constituting eachlogic element, and it will be readily appreciated by one skilled in theart that many different variations and combinations of components can beused to perform the logic function assigned to each logic element.However, a brief description of the operation of these common elementswill be helpful in understanding the operation of the digital controlsystem of this invention. A flip-flop is a two stage circuit having twostable states. In one state, the first stage conducts and the secondstage is cut off. In the other state, the sec- 0nd stage conducts andthe first stage is cut off. The flip-flops are illustrated as rectangleshaving a set section S and a reset section R. Input terminals areattached to the left side of the flip-flops, as illustrated in thedrawings, and output terminals are attached to the right side thereof.When an input signal or pulse is applied to the input terminal of the Ssection, the flip-flop is set and the desired output signal, typically alogic I, is provided at the S output terminal only. When an input signalor pulse is applied to the R input terminal, the flip-flop is reset" andthe desired output signal 1 is provided at the R output terminal only.Naturally, the S and R outputs must always have opposite logic levels. Asmall circle at the input of a logic element indicates that the elementresponds to a negative-going or trailing edge of a pulse applied at thatinput, whereas an uncircled input terminal indicates that the logicelement responds to a positive-going or leading edge of a pulse appliedat that terminal. A small circle at the output terminal of a logicelement indicates that the desired output signal will be negative-goingor logic 0, whereas an uncircled output indicates that adesired outputsignal will be positive-going or logic I. When an input signal or pulseis shown as applied to a terminal connected to the junction to the S andR sections, the element is intended to represent a clocked flip-flop,characterized by the fact that the stable state at the input of the Sand R sections will be shifted to the outputs of the S and R sectionsrespectively only upon the occurrence of a clock" pulse at the junctionterminal. A clocked type flip-flop will act as a binary counter. if theR output is connected to the S input and the S output is connected tothe R input (commonly known as the .I-K configuration). With these crossconnections, the flip-flop is set with each even numbered clock pulse atthe clock terminal and reset with each odd numbered pulse at the clockterminal. Clocked flipflops normally have an additional pair of inputterminals 8,, and R, for directly setting or resetting the flipflopwithout waiting for the occurrence of a clock pulse. In practice, a setflip-flop is said to be in the 1 state, while a reset flip-flop is inthe 0 state.

An OR gate as used herein produces a desired output I level signal inresponse to a 1 input signal at any of its input terminals, while an ANDgate produces a desired l output signal only in response to 1 levelinput signals at all of its input terminals simultaneously. When thedesired output signal is a logic 0, the gates are respectively termedNOR and NAND gates. An inverter (INV) converts a 1 level signal into a 0level signal and vice versa. Finally, certain logic functions in theembodiments to be described, such as binary counting and multiplexing,may be performed by multi-function logic elements which have beenstandardized in the digital art and which are available insingle-package integrated circuits. While these multi-function circuitsare characteristically combinations of simple flip-flops and gates,their operation is better understood by reference to the overallfunction and input-output characteristics. Thus the detailed descriptionof the internal construction of these elements is incorporated byreference to the manufacturer and his assigned type number for theelement.

GENERAL DESCRIPTION OF THE VARIOUS EMBODIMENTS AND THEIR OPERATIONTurning now to FIG. 1, a functional block diagram illustrates a digitalgovernor constituting an exemplary embodiment of the present invention.A prime mover to be governed is supplied from an energy source 12, therate of supply being regulated by a throttle valve 14 mechanicallycontrolled by an actuator 16. The prime mover 10 is shown mechanicallyconnected to drive a load 18 while additionally being connected toaspeed signal generator or transducer 20.

The prime mover 10 may, for example, be an internal combustion gasolineengine, in which case the energy source 12' would'be a gasoline supplyhaving an output conduit controlled by the throttle valve 14. Alternatively, the prime mover 10 may take the form of hydraulic turbine whoseload is an electric generator, in which event the energy source 12 maybe a source of pressure fluid from a hydraulic pressure head such as thepen stock of a power dam.

The primary purpose of a speed governor is to maintainthe speed of theprime mover 10 substantially constant at a selected set point speedregardless of variations in the load 18* and the torque it imposes onthe prime mover. Where the load is an electric generator, the torquevariations will be due to sudden changes'in the amount of current drawnfrom the generator. Similarly, if the prime mover is an engine fordriving a vehicle, the load 18 will vary due to changes in the terrainover which the vehicle passes. The conventional speed governor employs aspeed reference against which a signal proportional to the actual speedof the prime mover is compared to produce a speed error signal foradjusting the actuator, which in turn adjusts the rate of energy flowtothe prime mover to close the control loop.

In conventionalgovernors, either of two basic actuator types may beused, integrating or proportional." A proportional actuator ischaracterized by the fact that the position of the control throttle isat all times proportional to the magnitude of the signal suppliedthereto;

In contrast, an integrating actuator moves the throttle at a velocitydepending upon or proportional to the magnitude of the signal suppliedtheireto and by an amount determined by the time integral of theinputsignal.

The actuator 16 shown in FIG. 1 of the proportional type, an example ofwhich is shown and fully described in U.S. Pat. No. 3,442,277, issuedMay 6, 1969 to Bernard B. Barnes andassigned to the assignee of thepresent invention. Reference may be made to the above-identified patentfor a more complete explanation of the advantages of the proportionalacutators over integrating actuators.

The speed governor of the present invention departs considerably fromthe conventional speed governors discussed above, and, as will be morefully explained in the discussion to follow, applicants governor isreadily adaptable for operation as either a droop or non droop"(isochronous) governor, with the further advantage that theproportional-type actuator 16 may be used in either mode of operation.

As illustrated in FIG. 1, the governor of the present invention includesa reference signal generator 22 for producing a signal in the form of atrain of pulses having a reference frequency f, proportional to thedesired speed of the prime mover. The reference signal period t, is thusinversely proportional to the desired speed, bearing in mincl the basicand well known relationship that the period t of any recurring event orwave is equal to the reciprocal ofthe event or wave frequencyf, i.e.,t=l/f. This pulse train, along with a train of pulses from thetransducer 20 having a period t, or spacing inversely proportional tothe actual speed of the prime mover, is fed to a comparator-integratorunit 40 which produces a binary encoded servo control signal Z having anumerical magnitude proportional to the time integral of the differencebetween the respective periods t, and r, of the two pulse trains. Theservo control signal Z is then fed through a digital-to-analog converter46 to the proportional actuator 16 which correctively adjusts thethrottle l4, and thus the rate of energy flow and the speed of the primemover 10 so that the difference between the periods 1 and t of therespective pulse trains is reduced substantially to zero. The referencefrequency may, in different embodiments, represent the instantaneousdesired speed or the long term desired set point speed.

Although an exemplary form of the reference signal generator 22 will belater described, for the embodiment of FIG. 1 any of a wide variety ofsimple pulse generators known to the art may be employed. In onepreferred form, the generator 22 will supply a highly stable constant,but manually adjustable, frequency f, equal to the frequency f, of thespeed pulses when the prime mover is stabilized at the desired set pointspeed. In an alternative form to be described, the generator 22 mayprovide a reference frequency f, which changes quickly in response tovariable factors represented by signaled, changeable input numbers.

For the purpose of producing a train of pulses having a period varyingwith the speed of the prime mover, the speed signal generator 20 is inthe fonn of a speed-tofrequency converter or transducer, having amechanical input from the prime mover 10 which is effective to produce atrain of speed pulses on an output line 38 having a period t, whichvaries inversely in accordance with the speed of the prime mover. Thespeed signal generator 20 may, for example, comprise a toothed or gearwheel mounted for rotation by the prime mover 1 0 for cutting either alight path to a photosensitive pickup or a flux path of an inductivepickoff in a manner well known in the art. The electrical pulsesgenerated by the photoelectric or inductive pickup constitutethe'aforementioned train of speed pulses.

The signal comparator-integrator 40 is connected to receive thereference pulses on line 36 and the speed pulses on line 38. The device40 includes an input logic section 42 for effectively measuring therespective periods t and t, by selectively controlling the counting ofhigh frequency pulses during time segments proportional to t, and t, ina manner to be hereinafter described. The period measuring logicsupplies an input to an integrating counter-register combination 44which functions by successive iterations to perform the indicatedalgebraic functions, wherein e represents the instantaneous difference(measured at iteration time interval n) of the periods t, and 1,, C, isa multiplication factor, and the servo correction signal Z is a binarynumber representing the sum of the accumulated measurements of the timedifferece between the periods t, and t, or, effectively, the timeintegral of the period difference (t,,t,-). The control signal 2 iscoupled to the proportional actuator 16 through the digital-to-analog (Dto A) converter 46 to close the primary governor servo loop. The analogform of the digital signal Z is here designated Z to distinquish thetwo.

The system thus far described governs the speed in an isochronousmanner. A drop in the speed in the prime mover 10 due to an increase inload will produce a period difference t,,t, which, through amplificationand integration, will increase the control signal Z and the rate ofenergy flow through the valve 14 to return the prime mover to thedesired set point speed. Such a governor will control the engine speedsatisfactorily for certain engines in which induction loss is high. Forother prime mover configurations, however, an added degree of stabilityis desirable to prevent hunting or oscillation of the speed error,especially when overall system gain is high.

The embodiment of the invention shown in FIG. 2 provides this additionaldegree of stabilization by inclusion of a reference signal generator 22having operative elements responsive to the servo control Z for varyingthe period t, of the reference pulses in accordance with variations inthe control signal Z. To this end, the reference signal generator 22 isillustrated as being driven by a clock pulse source 26 andproviding afrequency division function,

fr fc 1 wherein f, is the constant frequency of the clock source 26, f,is the frequency of the reference pulse train and B is anon-dimensionalnumber representing the algebraic sum of a plurality of binary codedsignals provided at inputs 28 and 30 respectively. in the presentinstance,

where Z, received at input 30, is the binary coded servo correctionnumber previously described and R, received at input 28, is a set pointnumber which in this instance is a binary ls complement of a set pointnumber R signaled by a series of adjustable digit switches hereinafterdescribed. Since the frequency f, of the reference pulse train appearingon the output line 36 is inversely proportional tothe algebraicsummation number B,, an increase in the set point number R will cause adecrease in the frequency f, and therefore an increase in the period t,.In other words, the period t, is directly proportional to the manuallysettable number R.

At this point, and to avoid momentary confusion, it should be noted thatthe number R appears as a positive number in the expression B, R Zlabeled in FIG. 2. As will appear more fully below, the set point numberR is the l' complement of a true, conventional set point number R. Thebinary ls complementing device 29 is provided so that the frequency f,ries in sense with variations in the manual setting of R.

Similarly, as 2 increases, the divisor B increases and the period t, ofthe reference pulses increases. The period t, thus changes directly inaccordance with variations in the control signal Z. If the load 18 is asingle unit (and not an alternator connected to an infinite bus"), theresult of the feedback of Z on the path 47 will be to introduce a finitespeed error, or droop, to the system, the magnitude of which depends onthe load. As the servo control signal Z increases in response to a loadincrease on the prime mover 10, the period I, also increases to approachthe period t, and

v to restore the periods t, and t, to a condition of equality with eachother. As a result, the period difference t,-t,

will be quickly reduced before appreciable lags in the governor controlloop can introduce serious overshoot in the response.

As an additional feature of the invention, the digital governor systemshown in FIG. 2 as a droop type system may be readily expanded, byduplication of the same hardware building blocks and the adjustment ofconstants, into an isochronous system. Such a conversion has beenillustrated in the embodiments shown by FIG. 3 and FIG. 4, the lowerportion of each comprising a droop digital governor essentiallyidentical to that shown in FIG. 2. Focusing first on the embodiment ofFIG. 3, the upper portion of the drawing shows the functional blockdiagram ofwhat is, in effect, a second governor acting to control theoutput frequency f, of the reference signal generator 22 of the primarygovernor. Thus the functional blocks of the primary governor alreadydescribed are duplicated and the reference numbers remain the same asfor the identical elements of FIGS. 1 and 2.

Accordingly, the embodiment of FIG. v3 includes all the elements andproduces all the control signals of the embodiment of FIG. 2 but furtherincludes an auxiliary signal generator 50 settable to produce a thirdtrain of pulses at a predetermined fixed frequency f equal to thefrequency which the aforementioned reference and speed pulses willattain under no-load, droop-free conditions of the embodiment of FIG. 2.The period t, of this third train of pulses provides a standard for andis compared with the period t of the reference pulses in a secondcomparator-integrator 64 which produces a binary coded reference controlsignal Z having a numerical magnitude which varies in accordance withthe time integral of the difference between the respective periods t,and t The reference control signal Z is connected to the input 34 of thereference signal generator 22 in opposition to the servo control signalZ. The rate of integration of the second (upper) comparatorintegrator 64is chosen to be much slower than that of the first (lower)comparator-integrator 40 so that the reference control signal Z willgradually eliminate the effect of the servo control signal Z-on thefactor B, and thus on the period t, of the reference signal. Therefore,the upper portion of the embodiment of FIG. 3 effectively de-droops thedroop governor shown in the lower portion, but it does so at a ratewhich is too slow to interfere with the stabilizing effect provided bythe feedback of the servo control signal Z to the reference generator22. As such, the embodiment of FIG. 3 provides a reset or integralcorrection over the term.

The auxiliary generator 50 performs a frequency division function asindicated by the equations labeled in the frequency divider 52 and thereference control logic 54. Inputs 56, 58 are shown to illustrate acapacity for algebraic summation of binary signals in the generator 50,but in isochronous operation (with a switch open, as shown) the onlyinput signal to the control logic S4 is the speed set point number R,the auxiliary signal generator 50 producing an output frequency f fc/which remains constant at all times. The second comparator-integrator 64is connected to receive the reference pulses at a frequency f, from theprimary governor and the auxiliary pulses at a frequency f from theauxiliary generator 50 appearing on a line 66. Like thecomparator-integrator 40 of the primary governor, the device 64 providesa period measuring logic function, an error detection function, amultiplication or

1. In an electronic governor for controlling the speed of a prime moverby controlling the flow of energy thereto, the combination comprisingmeans including a transducer for producing a first train of pulsesspaced by a period ts which varies in accordance with the actual valueof said speed, a reference signal generator for producing a second trainof pulses having a period tr corresponding to a desired speed set point,signal comparison means coupled to said transducer and said referencesignal generator for producing a servo control signal Z digitallyrepresenting the numerical value of the time integral of the differencebetween the respective periods of said first and second pulse trainssuch that Z integral C(ts-tr)dt, means including an actuator responsiveto said servo control signal for correctively adjusting the rate of saidenergy flow to restore equality between the periods of said speed andreference pulses.
 2. An electronic governor for conTrolling the speed ofa prime mover by controlling the flow of energy thereto, comprisingmeans including a transducer for producing a first train of pulsesspaced by a period ts which varies in accordance with the actual valueof said speed, a reference signal generator for producing a second trainof pulses having a period tr corresponding to a desired speed set point,signal comparison means coupled to said transducer and said referencesignal generator for producing a servo control signal Z having amagnitude which varies in accordance with the time integral of thedifference between the respective periods of said first and second pulsetrains such that Z Integral C(ts-tr)dt, means including an actuatorresponsive to said servo control signal for correctively adjusting therate of said energy flow to reduce the time difference between therespective periods of said pulse trains to zero, and stabilizing meansoperatively associated with said reference signal generator andresponsive to said servo control signal for varying the period of saidreference pulses in accordance with variations in said servo controlsignal.
 3. An electronic governor according to claim 2 in which saidservo control signal is in binary coded form and digitally representsthe numerical value of the time integral of said period difference andwherein said means for adjusting the rate of said energy flow includes adigital-to-analog converter connected for receiving said servocorrection signal and for producing a dc. electrical signal of amagnitude proportional to the binary magnitude of said servo controlsignal, said d.c. signal being coupled to said actuator for effectingadjustment of the energy flow.
 4. An electronic governor for controllingthe energy flow to a prime mover to stabilize the speed thereof at adesired set point, comprising means including a transducer for producinga first train of pulses spaced in accordance with the actual value ofsaid speed, a reference signal generator for producing a second train ofpulses having a reference pulse frequency and period; signal comparisonmeans coupled to said transducer and said reference signal generator forproducing a servo control signal having a magnitude which varies inaccordance with the time integral of the difference between therespective periods of said first and second pulse trains, stabilizingmeans operatively associated with said reference signal generator andresponsive to said servo control signal for varying the period of saidreference pulses in accordance with variations in said servo controlsignal, means including an actuator responsive to said servo controlsignal for correctively adjusting the rate of said energy flow, wherebythe actual value of said speed tends to be maintained at a speedcorresponding to the period of said reference pulses, means including anauxiliary signal generator settable to produce a third train of pulsesat a frequency equal to the frequency of said first and second pulsetrains when said speed is stabilized at a desired set point value, andmeans connected to receive said second and third pulse trains forproducing a reference control signal varying in accordance with the timeintegral of the difference between the periods of said second and thirdpulse trains, said reference control signal being connected to saidreference signal generator in opposition to said servo control signalfor gradually eliminating the effect of said servo control signal on theperiod of said reference pulses.
 5. An electronic governor according toclaim 4 wherein said servo control and reference control signals areproduced in binary coded form and have binary magnitudes digitallyrepresenting the numerical values of said integrals of the respectiveperiod differences and wherein said reference signal generator and saidmeans for controlling the energy flow are adapted for response to Saidbinary coded signals.
 6. An electronic governor for controlling theenergy flow to a prime mover to stabilize the speed thereof at a desiredset point, comprising means including a transducer for producing a firsttrain of pulses spaced in accordance with the actual value of saidspeed, a reference signal generator for producing a second train ofpulses having a reference frequency and period, signal comparison meanscoupled to said transducer and said reference signal generator forproducing a servo control signal having a magnitude which varies inaccordance with the time integral of the difference between therespective periods of said first and second pulse trains, stabilizingmeans operatively associated with said reference signal generator andresponsive to said servo control signal for varying the period of saidreference pulses in accordance with variations in said servo controlsignal, means including an actuator responsive to said servo controlsignal for correctively adjusting the rate of said energy flow so thatthe difference between the periods of said first and second pulse trainsis reduced to zero, means including an auxiliary signal generatorsettable to produce a third train of pulses at a frequency equal to thefrequency of said first and second pulse trains when the said speed isstabilized at the desired set point, and means connected to receive saidfirst and third pulse trains for producing a reference control signalvarying in accordance with the time integral of the difference betweenthe periods of said first and third pulse trains, said reference controlsignal being connected to said reference signal generator in oppositionto said servo control signal for gradually eliminating the effect ofsaid servo control signal in varying the period of said second pulsetrain.
 7. An electronic governor according to claim 6 wherein said servocontrol and reference control signals are produced in binary coded formto digitally represent the numerical value of said respective measuredtime integrals and wherein said reference signal generator and saidmeans for controlling the energy flow are adapted for response to binarycoded signals.
 8. In an electronic governor for controlling the flow ofenergy to a prime mover to stabilize the speed thereof at a desired setpoint, the combination comprising means including a transducer forproducing a first train of pulses spaced in accordance with the actualvalue of said speed, a reference signal generator having an inputcircuit for simultaneously receiving a plurality of number-representing,multi-bit binary coded signals, an output terminal and means responsiveto said binary coded signals for producing at said output terminal asecond train of pulses spaced in accordance with the algebraic sum ofthe numbers represented by said binary coded input signals, manuallysettable means for producing a first one of said binary coded inputsignals with a numerical value corresponding to the desired set pointspeed, signal comparison means coupled to receive said first and secondpulse trains for producing a binary coded servo control signal digitallyrepresenting the numerical value of the time integral of the differencebetween the respective periods of said first and second pulse trains,and means including an actuator responsive to said servo control signalfor correctively adjusting the rate of said energy flow to reduce saiddifference between said respective periods to zero, said servo controlsignal additionally being coupled to said generator input circuit toprovide a second binary coded input signal whose numerical value isalgebraically summed with that of said manually settable binary signalto effect stabilization in the response of the governor to variations insaid speed.
 9. In an electronic governor, the combination according toclaim 8, further comprising an auxiliary signal generator settable toproduce a third train of pulses at a frequency equal to the frequency ofsaid first and second pulse trains when the actual value of said speedis stabilized at the desired set point speed; and means connected toreceive said second and third pulse trains for producing a referencecontrol signal digitally representing the numerical value of the timeintegral of the difference between the periods of said second and thirdpulse trains, said reference control signal being connected as a thirdbinary coded input signal to said generator input circuit in oppositionto said servo control signal for gradually eliminating the effect ofsaid servo control signal on the period of said second train of pulses.10. In an electronic governor, the combination according to claim 8,further comprising an auxiliary signal generator settable to produce athird train of pulses at a frequency equal to the frequency of saidfirst and second pulse trains when the actual value of said speed isstabilized at the desired set point speed; and means connected toreceive said first and third pulse trains for producing a referencecontrol signal digitally representing the numerical value of the timeintegral of the difference between the periods of said first and thirdpulse trains; said reference control signal being in binary form andconnected to said generator input circuit in opposition to said servocontrol signal for gradually eliminating the effect of said servocontrol signal on the period of said second train of pulses.
 11. In anelectronic governor for maintaining the speed of prime mover bycontrolling the flow of energy thereto, the combination comprising meansincluding a transducer for producing a first train of pulses spaced byperiods ts which vary inversely in accordance with the actual value ofsaid speed, a reference signal generator for producing a second train ofpulses having a reference period tr, signal comparison means includinga. a source of clock pulses at a high frequency, b. a multi-stage binarycounter having first and second clock input terminals for selectivelycontrolling the direction of counting in an up-count and down-countdirection respectively, c. a logic circuit coupled to receive said firstand second pulse trains and adapted to control the coupling of saidclock pulse source to said first and second clock input terminalsrespectively for intervals corresponding to the respective periods tsand tr of said speed and reference pulse trains, d. a holding registercontrolled by said logic circuit for samplng the contents of saidcounter at predetermined intervals to produce a binary coded controlsignal having a numerical magnitude which varies in accordance with theaverage value of the count in said counter, and means including anactuator responsive to said binary control signal for correctivelyadjusting the rate of said energy flow to reduce the time differencebetween the respective periods of said first and second pulse trains tozero.
 12. In an electronic governor for maintaining the speed of a primemover by controlling the flow of energy thereto, the combinationcomprising means including transducer for producing a first recurringsignal having a period ts which varies inversely according to changes inthe actual value of said speed; a reference signal generator forproducing a second recurring signal having a reference period tr; perioddifference integrating means including an up-down binary counter and acounter logic circuit selectively controlling the direction of counting,said logic circuit being responsive to said first and second signals andcausing said counter to count up and down respectively for intervalscorrespondng to the non-overlapping portions of partially overlappingrespective periods ts and tr; a digital register means for sampling andholding the counter contents at the end of each up-and-down operatiOn ofsaid control logic circuit, said register having output means forproducing a servo control signal digitally representing the numericalvalue of the time integral of the difference between said periods; andmeans including an actuator responsive to said servo control signal forcorrectively adjusting the rate of said energy flow to reduce the timedifference between respective periods of said pulse trains to zero. 13.The combination defined in claim 12 wherein said counter logic circuitis operative during each up-and-down operation to inhibit counting ineither direction during the interval of timing overlap of the respectiveperiods ts and tr so that unnecessarily large excursions by the counterare prevented.
 14. The combination defined in claim 12 further includinga source of clock pulses for driving said counter in an up-count ordown-count directon under the control of said counter logic circuit andwherein the rate at which said servo control signal changes in responseto a given difference between the respective periods ts and tr isdependent only upon the frequency of said clock pulses.
 15. Thecombination defined in claim 11 wherein the frequency of said clockpulses is several orders of magnitude higher than the frequencies of thesaid first and second signals, and wherein said summing means operatesat a gain factor C dependent only upon said clock pulse frequency, theservo control signal having an average value of Sigma C(ts-tr) where C(ts-tr) is the net change in the counter number resulting from eachup-and-down operation.
 16. An electronic governor for maintaining thespeed of a prime mover by controlling the flow of energy thereto,comprising means including a transducer for producing first recurringsignal having a period ts which varies inversely according to the actualvalue of said speed, means including a reference signal generator forproducing a second recurring signal having a reference period tr, signalcomparison means coupled to said transducer and said reference signalgenerator for producing a servo control signal having a magnitude whichvaries in accordance with the time integral of the difference betweenthe respective periods ts and tr of said first and second signals, saidcomparison means including a. an up-down counter, b. a source of clockpulses of a given frequency, c. means for causing said counter in effectto count the clock pulses up during successive ones of said periods tsand down during successive ones of said periods tr, and d. means forperiodically reading out the contents of said counter at the end ofup-down cycles to thereby produce a servo control signal numericallyrepresenting said time integral, and means including an actuatorresponsive to said servo control signal for correctively adjusting therate of said energy flow to reduce the time difference between therespective periods of said pulse trains to zero, whereby the servocontrol signal varies with an average value equal to Integral C (ts-tr)and the gain factor C is entirely independent of the frequencies andperiods of the first and second signals.
 17. The combination set forthin claim 5 further characterized in that said signal comparison meansincludes a. an up-down counter b. a source of clock pulses c. means forcausing said counter in effect to count the clock pulses upwardly anddownwardly respectively during the periods of said first and secondtrains of pulses so that the net change in the counter contents is equalto the difference in the respective periods multiplied by a factor Cproportional to the clock pulse frequency, and d. means for reading outthe contents of said counter after each up-down count cycle to form saidservo control signal which thereby is affEcted in gain only by the clockpulse frequency and not by the frequencies or periods of said first andsecond trains.
 18. In a governor for controlling the rate of energyinput to a prime mover to control its speed, the combination comprisingmeans for producing a signal having a parameter varying in accordancewith the actual value of said speed, means for producing a second signalhaving a reference parameter adjustable or variable in accordance withthe desired speed set point, means responsive to said first and secondsignals for producing a servo control signal digitally representing achangeable number and for updating said number during successiveiteration periods by an amount which is the product of a gain factor andthe difference between the parameters of said first and second signals,and means for varying said rate of energy input according to the averagevalue of the number represented by said servo control signal.
 19. In agovernor for controlling the rate of energy input to a prime mover tocontrol its speed, the combination comprising means for producing afirst signal having a first parameter varying in accordance with theactual value of said speed, means for producing a second signal having areference parameter adjustable or variable in accordance with thedesired value of speed, a source of clock pulses having a clockfrequency, a reversible counter, means responsive to said first andsecond signals for causing said counter to count said clock pulsesupwardly and downwardly during different time portions of repeatingcount operation cycles, the up portion of each counting cycle beingproportional to said first parameter and the down portion beingproportional to said reference parameter, means for periodically readingout the number contents of said counter to signal a periodically updatedservo control number which in average value varies as the time integralof the product of a gain constant C times the difference between saidfirst and reference parameters, and means for making said rate of energyinput proportional to said signaled servo control number, whereby thegain constant C is determined by and is proportional to the clock pulsefrequency and is independent of the values of the first and referenceparameters.
 20. A speed governor for controlling the rate of energy flowto a prime mover to maintain the speed thereof at a desired set point,comprising in combination manually settable means for producing a firstsignal having a parameter corresponding to a desired set point speed,means associated with said prime mover for producing a second signalhavng a parameter varying with the actual value of said speed, servocontrol means connected to receive said first and second signalsincluding a digital signal comparator and amplification device forproducing a control signal having a magnitude proportional to thedeparture of said second signal from said first signal, servo meansincluding an actuator coupled to said servo control means forcorrectively adjusting and maintaining said flow of energy at a rateproportional to the magnitude of said control signal, and trim meansconnected to receive said first and second signals for generating athird signal having a parameter which varies in accordance with the timeintegral of speed departures from the desired set point, said thirdsignal being connected to said servo control means to effect a gradualadjustment of said servo control signal and thereby to restore theactual value of said speed to the desired set point, said servo controlmeans being operative to produce said control signal with a high degreeof amplification which is independent of the set point or actual speed.21. An electronic governor for controlling the flow of energy to a primemover to stabilize the speed thereof comprising manually settable meansfor generating a first binary coded signal correspOnding in numericalvalue to a desired set point speed, means including a transducer forproducing a train of speed pulses having a frequency varying with theactual value of said speed, reference generating means for producing atrain of reference pulses, comparison means adapted to receive saidactual value and reference pulses for producing a second binary codedsignal corresponding to deviations in the actual value of said speedfrom the desired set point, means including an actuator responsive tosaid second binary coded signal for adjusting the rate of said energyflow to correct for said speed deviation, said reference generatingmeans including a variable frequency oscillator responsive to said firstand second binary coded signals and operative to produce said referencepulses at a frequency which varies in accordance with the algebraic sumof said binary coded signals.
 22. In a system for controlling the rateof energy input to a prime mover to govern the speed of the latter, thecombination comprising means for producing a first signal having aparameter which varies according to the actual value of said speed,means for producing a reference signal having a variable parameterindicative of the instantaneously desired speed, means responsive tosaid signals for iteratively signaling in numerical form the error econstituted by the difference between the parameter values of the firstand second signals, means coupled to said signaling means for signalingplural bits which in binary or coded binary notation represent aniteratively updated number Z which changes during successive iterationsaccording to the relation Zn Zn 1+ C e where C is a gain factor and ndesignates the successive iteration periods, and means responsive tosaid signaled bits for making said rate of energy input proportional tothe number Z.
 23. In a system for controlling the rate of energy inputto a prime mover to govern the speed of the latter, the combinationcomprising means for producing first recurring signals having a periodts inversely related to the actual value of said speed, a referencesignal generator having means to produce second recurring signals havinga reference period tr, means responsive to said first and referencesignals for signaling plural bits which in binary or binary codednotation represent an iteratively updated number Z which changes duringsuccessive iterations according to the relation Zn Zn 1+ C (ts - tr)nwhere C is a gain constant and n designates the successive iterationperiods, and means responsive to said plural bit signals for varyingsaid rate of energy input in accordance with variations of therepresented number Z.
 24. In a system for controlling the rate of energyinput to a prime mover to govern the speed of the latter, thecombination comprising means for producing first recurring signalshaving a period ts inversely related to the actual value of said speed,a reference signal generator having means to produce second recurringsignals having a reference period tr, means responsive to said first andsecond signals for signaling a first set of plural bits which in binaryor binary coded notation represent an iteratively updated number Z whichchanges during successive iterations according to the relation Zn Zn 1 +C (ts - tr)n where C is a gain factor and n designates the successiveiteration periods, means responsive to said plural bit signals forvarying the said rate of energy input in accordance with variations ofthe represented number Z, and means coupled to receive said plural bitsignals and responsive thereto for causing the reference period tr ofsaid second signals from said generator to vary in accordance withvariations of the represented number Z.
 25. The combination set forth inclaim 24 further characterized in that said last-named means comprisesmeans for causing said generator to vary the period tr according to therelation: tr A + Z/ fc where A is the composite sum of other numberswhich may be constants or variables and fc is a fixed or variableproportionality factor.
 26. The combination set forth in claim 25further characterized in that A is equal to R, and R is a numberrepresenting set point speed in a relationship wherein increases in Rcorrespond to decreases in set point.
 27. The combination set forth inclaim 25 further characterized in that A is equal to R - Z'', where R isa number representing desired set point speed in a relationship whereinincreases in R correspond to decreases in set point, and Z'' is a numberwhich varies as the time integral of the difference (tr-ta), the periodta being directly variable according to changes in R.
 28. Thecombination set forth in claim 27 further characterized in that theperiod ta is directly variable according to changes in the sum R + Z.29. In a system for controlling the rate of energy input to a primemover to govern the speed of the latter, the combination comprisingmeans for producing first recurring signals having a period ts inverselyrelated to the actual value of said speed, a reference signal generatorhaving means for producing second recurring signals having a referenceperiod tr, means responsive to said first and second signals forsignaling plural bits which in binary or binary coded notation representan iteratively updated number Z which changes during successiveiterations according to the relation Zn Zn 1 + C1 (ts - tr)n where C1 isa gain constant and n designates the successive iteration periods, meansresponsive to said plural bit signals for varying said rate of energyinput in accordance with variations of the represented number Z, meansfor producing auxiliary recurring signals having a period ta, meansresponsive to said second and auxiliary signals for signaling a secondset of plural bits which in binary or binary coded notation represent asecond iteratively updated number Z'' which changes during successiveiterations according to the relation Z''n Z''n 1 + C2(tr - ta)n where C2is a gain factor and n designates the successive iteration periods, andmeans responsive to said first and second sets of plural bit signals forcontrolling said reference signal generator to vary said referenceperiod tr according to changes in the sum (Z - Z'').
 30. The combinationset forth in claim 29 further including means for producing a third setof plural bit signals representing an adjustable set point number R,means associated with said auxiliary signal producing means andresponsive to said third set of bit signals for causing the period ta tovary directly according to the value of the number R, and said means forcontrolling said reference signal generator including means responsiveto said first, second and third sets of bit signals for varying saidreference period tr according to changes in the sum R + Z - Z''.
 31. Thecombination set forth in claim 30 further characterized in that saidmeans associated with said auxiliary signal producing means includesmeans responsive to said first and third sets of bit signals for causingthe period ta to vary directly according to the value of the sum R + Z.32. The combination set forth in claim 29 wherein the factor C1 isgreater than the factor C2.
 33. In a system for controlling the rate ofenergy input to a prime mover to govern the speed of the latter, thecombination comprising means for producing first recurring signalshaving a period ts inversely related to the actual value of said speed,a reference signal generator having means to produce second recurringsignals having a reference period tr, means responsive to said first andsecond reference signals for signalling a first set of plural bits whichin binary or binary coded notation represent an iteratively updatednumber Z which changes during successive iterations according to therelation: Zn Zn 1 + C1 (ts -tr)n where C1 is a gain constant and ndesignates successive iteration periods, means responsive to said firstset of plural bit signals for varying said rate of energy input inaccordance with variations in the represented number Z, means forproducing auxiliary recurring signals having a perDwd ta, meansresponsive to said first and auxiliary signals for signaling a secondset of plural bits which in binary or binary coded notation represent aniteratively updated number Z'''' which changes during successiveiterations according to the relation Z''''n Z''''n 1 + C2(ts -ta)n whereC2 is a gain factor and n designates the successive iteration periods,and means responsive to said first and second sets of bit signals forcontrolling said reference signal generator to vary said referenceperiod tr according to changes in the algebraic sum (Z - Z'''').
 34. Thecombination set forth in claim 33 further including means to vary theauxiliary reference period ta in accordance with a signaled set pointnumber R, and said means for controlling said reference signal generatorincludes means responsive to said first and second sets of bit signalsand the signaled number R for varying the reference period tr inaccordance with changes in the sum R + Z - Z'').